1. Field of the Invention
The present invention relates to an image display apparatus for displaying data in an information processing device, such as computers, as a visible image using an electrophotography.
2. Description of the Prior Art
Image display apparatuses for displaying data in computers, facsimiles and the like are generally of a cathode ray tube (CRT) type. In place of such image display apparatuses, the applicant has proposed an image display apparatus which comprises an image bearing web in the form of an endless moving belt (U.S.S.N. Nos. 445070, 509767 and 525212).
The image display apparatus proposed by the applicant is shown in FIG. 1 which comprises a casing 1 and an endless belt-shaped photosensitive web 8 movably mounting within the casing 1. The photosensitive web 8 is intermittently driven by drive means (not shown) and guided by guide rolls 9, 10, 11 and 12. There is provided a semiconductor laser (not shown) ehich is adapted to generate output light beams modulated by electric image signals. The output light beam impinges on the inner face of the photosensitive web 8 and scan in one direction the same by a scanner 8 through a f-.theta. lens 6 and mirror 7. The photosensitive web 8 may consist of a transparent, electrically conductive substratum and a photoconductive layer formed thereover.
In an exposure position A, a development device 15 is disposed in opposition to the outer face of the belt-shaped photosensitive web 8 and comprises a sleeve 17 within which a magnet 16 is mounted to rotate in the direction shown by an arrow in FIG. 1. An electrically conductive and magnetic developer (toner) 18 is supplied to the surface of the sleeve 17 and will contact with the surface of the photosensitive web 8 after the toner layer has been uniformly regulated by a blade 19. DC voltage is applied across the sleeve of the development device and the substratum of the photosensitive web 8. Adjacent to the exposure and developement position there are located rollers 13 and 14 which serve to maintain the photosensitive web 8 flat so that the gap between the photosensitive web surface and the sleeve of the development device will exactly be kept constant. An image is written on the surface of the photosensitive web in the position A by the use of light beam and then developed into a toner image which will be fed to a display section 2.
The display section 2 includes a rectangular window 3 formed in the front face of the casing 1 and a transparent member 4, such as glass or resin mounted over the window 3 through which the toner image on the photosensitive web can be observed externally. The photosensitive web 8 may be stopped automatically or manually for a given period of time if a predetermined location thereof on which the visible image is formed reaches the region of the window 3. In this manner, the toner image on the photosensitive web 8 surface can be observed at the window 3 through the transparent member 4.
The image display apparatus further comprises a lamp 20, if necessary, for erasing any hysteresis which possibly remains on the photosensitive web 8. The lamp 20 is in its ON state only when the photosensitive web 8 is being moved, and it is turned OFF with the stop of the web 8.
When a display of another information is desired, the photosensitive member 8 is again moved, and the photosensitive member having a previous image can be used as it is. There is no need of cleaning the toner of the previous image.
The principle of the operation is disclosed in the above-mentioned U.S.S.N. Nos. 445070 or 525212. So, a detailed explanation is omitted for the sake of simplicity, but the operation is described briefly in conjunction with FIGS. 2 and 3.
FIG. 2 shows the state of charge in the bright area of information light. When the toner 18 contacts the photosensitive web 8 while a voltage is being applied to the toner through the sleeve 17, an electrical field is applied to the photoconductive layer 8c. At this time, if the information light is projected, photo-carriers e are produced in the photoconductive layer 8c and then moved to near the surface of the photoconductive layer 8c under the action of the electric field. As a result, a strong electrostatic attraction force acts between the toner 18 carried on the sleeve 17 by the magnetic force of rotating magnet 16 and the photoconductive layer 8c so that the toner 18 will be diposited on the photoconductive layer 8c, that is, the surface of the photosensitive web 8. The sleeve 17, instead of the magnet 16, may be rotated.
In the illustrated apparatus, the photoconductive layer 8c is of an N-type semiconductor, while a positive voltage is applied to the toner 18. The photo-carriers e, which have been produced near the substratum in the photoconductive layer 8c on the irradiation of the information light LB, can satisfactorily be moved toward the photoconductive layer 8c. As a result, the toner 18 can be deposited on the photosensitive web 8 under the action of the strong electrostatic attraction force between the toner 18 and the photosensitive web 8.
FIG. 3 shows the state of charge in the dark area. When an electric field is applied across the toner 18 and the transparent conductve layer 8b of the substratum, an electrostatic attraction force is produced therebetween. However, this electrostatic attraction force is relatively small since the toner 18 and the conductive layer 18b are spaced away from each other by the photoconductive layer 8c. The toner 18 is therefore forced to separate from the photoconductive layer 8c, that is, the photosensitive web 8 due to various causes such as the magnetic force of the rotating magnet 16 within the fixed sleeve 17, and the attracting force acting among particles in the toner 18 and so on.
If it is desired to effect the change of toner image on the photosensitive web 8, a new image can be formed thereon simply by causing the photosensitive web 8 to pass by the exposure and development position. In other words, if the toner holding portion of the photosensitive web is to be changed to a non-toner-holding portion, the toner 18 reduced in its electrostatic attraction force is removed from the photosensitive web 8 under the influence of the magnetic field in the magnet 16 to provide a bright area on which no toner is deposited. On the other hand, if the toner holding area of the photosensitive web 8 is to be kept as it is, photo-carriers e are again injected under the action of information light so that new toner 18 will be attracted to the photosensitive web 8 against the action of the magnetic field to keep the toner thereon. Thus, the toner image on the photosensitive web 8 will not influence the subsequent formation of image. This means that an additional cleaning means is not required in the image display apparatus.
As shown in FIGS. 2 and 3, the image display apparatus further comprises a polyethylene terephthalate film 8a supporting the conductive layer 8b and a source of voltage E for the sleeve.
The photoconductive layer may be of ZnO, Se, SeTe, As.sub.3 Se.sub.2 or the like as well as CdS.
In the aforementioned arrangements of the image display apparatus, the image bearing web in the form of the belt-shaped photosensitive or heat-sensitive web on which an image is to be formed is repetitively used. As will be clearly seen from the drawings, the photosensitive member 8 is repeatedly bent or deformed. This affects the service life of the photosensitive member 8. It is subjected to repeated stresses so that crack, damage or peeling could happen thereto with the result of no function of the image bearing. Also, since it is a belt, prevention has to be considered as to the oblique belt movement, which prevention would result in a complicated structure. Additionally, there is a problem of the toner scattering which may be caused by the rotation of the belt.